Shipping pallets are well known in the art. Pallets are typically made of wood and used for supporting various items. They are constructed to be handled with a forklift or similar lifting device within a plant, a warehouse, or loading dock. There are several disadvantages to wood pallets. These disadvantages include the weight of the pallet and their susceptibility to breakage during use. In addition, wood is subject to deterioration that occurs with age and exposure to weather. Wood is also subject to attack by insects, mold and bacteria. There is the potential for damage to the pallet caused by spills from the goods that the pallets are bearing, for example a chemical spill or even physical damage from heavy loads. As a result, pallets are often discarded at waste sites and landfills. Contaminated wood pallets may present potential environmental hazards. The limited availability of the natural resources used to make the wood pallets is also a concern in many parts of the world. Also, wood pallets are not very hygienic for food and medical applications.
Metal pallets are also available, but have several drawbacks including their expense, susceptibility to corrosion, potentially poor chemical resistance and weight. When corroded, metal pallets are not very hygienic for food or medical applications either.
There have been many attempts to produce plastic pallets which are available in numerous shapes and forms. Industry has looked to plastic as an alternative to wood or metal for a number of reasons including the superior chemical resistance of plastic over wood or metal, the hygienic quality of plastic over wood or metal, the weight advantage of plastic, and the fact that some configurations of plastic pallets are less expensive to manufacture. In addition, plastic provides a major uniformity and consistency advantage in material over wood.
U.S. Pat. No. 5,704,300 describes a plastic pallet which is held together with mechanical fasteners. U.S. Pat. Nos. 5,527,585 and 5,405,567 describe plastic molded load-bearing structures. These patents describe structures fabricated from usually dissimilar plastic materials such as a deck sheet with downward extending feet that may be made removable so as to have a snap fit attachment.
Other patents describing plastic pallets of particular shapes and designs include U.S. Pat. Nos. 5,456,189; 5,505,141; 5,197,395; 4,843,976; 4,482,051 (Pat. No. Re. 32,530); 4,051,787; 3,989,156; 4,809,618; 4,799,433; 3,938,818; 3,938,448; 3,835,792; 3,702,100; 3,700,205; 3,610,172; and 3,603,272. The foregoing patents describe the advantages of a plastic pallet over the prior art wood pallet and describe pallets of various designs and shapes as well as methods for forming them.
Another approach has been to provide plastic laminates or panels such as taught in U.S. Pat. No. 5,219,629. Alternately, there have been attempts to make composite structural systems from plastics or some other reinforced composite material as described in U.S. Pat. Nos. 4,230,049 and 5,435,954. Other patents of interest that teach and describe fabricating or molding various shapes using plastic material include U.S. Pat. Nos. 5,547,081; 5,312,858; 5,259,169; 5,238,633; and 3,917,108.
U.S. Pat. No. 3,878,796 describes a plastic pallet assembly which includes boards and stringers that are held in an interlocked relationship with an arrangement of integral notches and shoulders.
There still exists a need for a plastic pallet that is simple in construction and easy to fabricate that has load bearing capability at least comparable to a wooden pallet. The plastic pallet would preferably have extruded thermoplastic members which are economical and lightweight. Advantageously, the extruded members include thermoplastic deck boards and stringers which provide design flexibility in fabricating pallets of various configurations and sizes. The plastic pallet may include stringers that have end caps that seal the ends of the extruded profiles and which provide added strength and durability. Preferably, the pallets would be constructed of a thermoplastic material that allows for a long useful life and complete recycling. The plastic pallet preferably would be constructed using a joining technology that does not require mechanical fasteners. Preferably such a plastic pallet would include ridges or other non-slip members on its deck boards and/or stringers. The ridges or other members may function to reduce slippage. The ridges may also function as energy concentrators for welding, may provide adhesive gap control when adhesives are employed as the joining technology, and may serve as mechanical interlocks during pallet storage and shipment. Preferably, the plastic pallet configurations may allow either four-way fork entry or two-way fork entry by a forklift or hand truck to facilitate stacking, lifting, and handling of the pallet. The profiles of the deck boards may in some embodiments include chamfers at desired locations for facilitating fork entry and exit from the pallet.